Drum for a production unit for a non-woven material, method for production of a non-woven material and non-woven material obtained thus

ABSTRACT

The invention relates to a production unit for non-woven material, comprising a spunbond tower ( 21 ), the conveyor ( 22 ) of which supplies the non-woven material preform to a drum ( 24 ) with a compartment ( 26 ) for aspirating said perform and applying the same to the lateral surface of the drum before the preform is hydraulically tangled by injectors ( 25 ). Said method permits the production of non-woven materials with uniform properties.

The present invention relates to nonwoven materials and their methodsand units of production.

U.S. Pat. No. 6,321,425 describes a method of fabricating a nonwovenmaterial which consists in sending a material, originating from aspunbond tower which normally comprises successively from top to bottoma generator of a curtain of filaments, in particular plastic filaments,a slotted attenuator device for drawing the filaments of the curtain, adiffuser and a conveyor for receiving the filaments, to a calender whichconsolidates the formed material preform, then to a water jet tanglingdrum. This method has the disadvantage of adversely affecting theuniformity of the formation of the material and of orienting thefilaments preferentially in the machine direction by the drawing whichis applied thereto.

The invention remedies this disadvantage by making it possible to obtaina nonwoven material whose properties are substantially isotropic, thatis to say substantially identical whether it be in the machine directionor in the cross direction.

This is achieved with a drum comprising a fixed cylindrical body withperforated lateral surface surrounded by a holed sleeve driven inrotation relative to the axis of the cylindrical body, and meansintended to create a partial vacuum inside the body. According to theinvention, a water-impermeable partition subdivides the interior of thebody into two compartments delimited by the partition and respectivelyby a first and a second portion of the lateral surface and both placedunder partial vacuum by the means intended to create same.

The first compartment of the drum according to the invention is used tobring onto the drum a material preform that lies on an associatedconveyor, substantially tangential to the drum at a so-called contactpoint (this is the point at which the conveyor and the drum are closestto one another without actually touching), even if this material preformis still slightly consolidated, as is the case when it is a materialcoming from a spunbond tower, without previously needing to calender thematerial preform or other operations subject it to involving a drawingoperation which definitively damage the isotropy of the properties ofthe nonwoven material finally obtained.

Preferably, the first compartment begins opposite the point of contactof the conveyor tangential to the drum and ends opposite a point of thelateral surface downstream, in the direction of rotation of the sleeve,of the point of contact. As soon as the material preform has thus beenapplied to the drum by the partial vacuum existing in the firstcompartment, it is subject to the water jet tangling.

According to one embodiment, the first compartment extends over acylindrical sector of the body defined, in the transverse sectional viewof the cylindrical body, substantially by two radii perpendicular to oneanother, the first compartment thus substantially occupying a quarter ofthe interior of the body. Preferably, the cylindrical sector occupied bythe first compartment is disposed in the second quadrant between 3 and 6o'clock.

The means intended to create a partial vacuum may be common to the twocompartments but, according to a preferred embodiment, each compartmenthas its own means of creating a partial vacuum and, preferably, thepartial vacuum is more intense in the first compartment than in thesecond. In particular, a partial vacuum lying between 30 and 400 mbarcan in particular be created in the first compartment and a partialvacuum lying between 30 and 300 mbar in the second compartment.

So that the drum can properly take hold of the material preform, it isbest that the ratio of the total area of the perforations, per unit ofsurface, to the area of the lateral surface on which they lie is greaterfor the first compartment than for the second. This ratio may be between5% and 30% for the first compartment whereas it is between 2% and 15%for the second compartment.

The perforations of the lateral surface opposite the second compartmentare in particular slots which lie opposite pressurized water injectorson the portion of the sleeve that passes just opposite the portion ofthe lateral surface of the second compartment. The pressure of the jetsis usually between 30 and 400 bar and the diameter of each jet between75 and 200 microns. A rigid rotating perforated roll is mounted on theexterior of the fixed cylindrical body and its interior diameter isadjusted to the exterior diameter of the cylindrical body so that theminimum clearance thus preserved allows rotation while minimizing airleaks. According to the technical solution used for the fabrication ofthis rotating roll, it is envisaged that plastic battens mounted onsprings are used to improve the separation seal of the two compartments.This rotating roll may be a simple perforated metal sheet, a roll madeof bronze or of stainless steel pierced with holes helically disposed, ahoneycomb roll. This may be a tube made of rolled perforated sheet metalcovered by a drainage sleeve made of coarse metal material whichprovides a good uniformity of water extraction. This rotating rollsupports a thinner perforated sleeve which effectively supports thefilaments and the fibers of the nonwoven during the hydraulic tangling.The holes in the sleeve may be randomly distributed. The holes may alsobe arranged in lines or in staggered fashion. The sleeve holes may alsobe distributed in small areas of arranged perforations distributedrandomly on the surface of the sleeve. The sleeve may consist of a metalmaterial or of a synthetic material or of a mixture of metal materialand synthetic material. Preferably the diameter of the sleeve holesshould be between 50 and 500 microns. To obtain patterns on thematerial, provision can also be made to slip an open-work sheath overthe sleeve, the openings of which having at least one dimension greaterthan 2 mm.

A further object of the invention is a unit for production of a nonwovenmaterial comprising a spunbond tower with conveyor leading to a drumaccording to the invention. Preferably, the tower conveyor and theconveyor tangential to the drum are one and the same conveyor, but it isalso possible to provide two distinct conveyors.

According to a particularly preferred embodiment, the drum is mounteddirectly downstream of the tower. In this specification, directlydownstream means without the interposition of a device provoking thedrawing of the material. There is therefore no calender, but there maybe a compactor cylinder.

A further object of the invention is a method for production of anonwoven material, which consists in using a unit according to theinvention and in adjusting the speed of the tower conveyor or of thetangential conveyor to a value greater than the linear speed of the drum(calculated on the circumference of the drum). This produces a nonwovenmaterial whose ratio of the breaking strength in the machine directionto that in the cross direction may be less than 1 due to this differencein speed. When the speeds are substantially the same, a ratio of lessthan 1.2 and of particularly approximately 1 of the breaking strength inthe machine direction to that in the cross direction of the nonwovenmaterial according to the invention can be obtained such that thenonwoven material according to the invention is particularly wellisotropic.

In the appended drawings, given as an example:

FIG. 1 is a view in perspective with partial cutaway of a unit accordingto the invention

FIG. 2 and FIG. 3 are two views in perspective with partial cutaway of adrum according to the invention

and FIGS. 4 and 5 are two schematic views of two variants of the unitaccording to the invention.

The drum represented schematically in FIG. 1 comprises an internal body1 consisting of a fixed roll with a diameter of 400 mm and of a metalsheet forming the lateral surface. The lateral surface is perforatedwith perforations of a diameter of 8 mm in one portion which willdelimit what will later be called the first compartment and the lateralsurface is pierced with several slots particularly opposite theinjectors in a portion which will delimit what will later be called thesecond compartment. The ratio (void fraction) of the sum of the areas ofthe perforations to the total lateral surface area is between 5% and 30%in the first compartment and between 2% and 15% in the secondcompartment. A perforated rotating roll 4 is slipped over the body 1 andis driven in rotation by a belt drive device 2. The roll 4 is holed. Theratio of the sum of the areas of the holes to the total lateral surfacearea of the roll 4 is between 30% and 90% and preferably between 40% and80%. The roll 4 has a thickness of between 1.5 and 30 mm and is usuallymade of stainless steel or of bronze. A sleeve 5 is slipped over therotating roll 4. The ratio of the sum of the areas of the holes to thetotal lateral surface area of the sleeve 5 is between 5% and 20% andpreferably between 5% and 15%. The sleeve 5 is obtained by nickelelectroplating. It is microperforated with holes of a diameter from 5 to500 microns and preferably between 200 and 400 microns. It has athickness of between 0.1 and 0.6 mm and preferably between 0.2 and 0.4mm. The inside of the drum 1 communicates with a duct 7 for extractingthe air and the water. Two injectors 8 and 9 respectively send jets ofwater toward the sleeve 5 along generatrixes of the body 1.

FIG. 2 is a view in perspective better illustrating an embodiment of thedrum. It consists of an inner roll 1 with axis O which is slotted as isthe metal sheet forming the lateral surface along two slots 11 disposedbetween braces 12 and lying in the quadrant between 1 o'clock and 3o'clock. In the quadrant from 3 o'clock to 6 o'clock a partition isarranged consisting of two metal sheets 13, 14 together forming a rollsector. The two metal sheets 13, 14 extend along a view in transversesection perpendicular to the axis O substantially along two radii. Theyare water-impermeable. They delimit between them with the portion 15 ofthe lateral surface lying between 3 o'clock and 6 o'clock a firstcompartment 16 while the partition 13, 14 delimits with the rest of thebody 1 a second compartment 17 into which the slots 11 open. Rows ofholes 18 made on the portion 15 of the lateral surface open into thefirst compartment 16. The first compartment 16 is connected to meansused to place it under partial vacuum. They are of the same type as theduct 7, but are distinct from it. The void fraction of the portion 15 is16%. It is greater than that corresponding to the slots 11. In onevariant, the first compartment also comprises a slot (not shown), placedat 6 o'clock opposite the point of tangency of the conveyor transportingthe preform of nonwoven with the roll. The purpose of this slot is tofacilitate the transfer of the filament material onto the portion of theroll facing the first compartment.

The embodiment represented in FIG. 3 is identical to that in FIG. 2,except that the rows of holes 18 of the portion 15 are replaced by slots19 which are not parallel with the axis O.

The unit represented in FIG. 4 comprises a spunbond tower 21 withconveyor 22 leading, with where necessary the interposition of a presserroll 23, to a drum 24 according to the invention. The conveyor 22 istangential to the drum 24 at the lowest point of the latter. Two waterinjectors 25 are provided opposite the portion of the lateral surface ofthe second compartment. One of the water injectors 25 is disposedangularly in a manner immediately adjacent to the first compartment 26,which means that one of the radial walls defining the second compartment26 lies in a position substantially corresponding to 4 o'clock while thefirst injector 25 lies in a position slightly before 4 o'clock. Thepreform of nonwoven material that is deposited on the conveyor 22 isaspirated onto the drum 24 thanks to the aspiration supplied by thefirst compartment 26, is tangled hydraulically by the injectors 25 andleaves the drum 24 to pass onto an inclined conveyor 27 before enteringan oven 28 and then leaving it to be rolled on a roller 29.

FIG. 5 again shows a spunbond tower 31 which deposits a preform ofnonwoven material 32, which is taken hold of by a first drum 33according to the invention having an injector 34 and which is sent by aconveyor 35 to a second drum 36 according to the invention.

FIG. 6 shows a variant of FIG. 4 in which the filament material istransferred to additional drums 41 and 42 to apply further consolidationand patterns to it before it enters the oven for drying by traversingair.

1. A drum comprising a fixed cylindrical body with perforated lateralsurface surrounded by a holed roll driven in rotation relative to theaxis (O) of the cylindrical body, and means intended to create a partialvacuum inside the body, characterized by a water-impermeable partitionsubdividing the interior of the body into two compartments delimited bythe partition and respectively by a first and a second portion of thelateral surface and both placed under partial vacuum by the meansintended to create same.
 2. The drum as claimed in claim 1,characterized in that it is associated with a conveyor tangential to thedrum at a point of contact and the first compartment begins opposite thepoint of contact and ends opposite a point of the lateral surfacedownstream, in the direction of rotation of the sleeve, of the point ofcontact.
 3. The drum as claimed in claim 2, characterized in that thefirst compartment extends over a sector of the body.
 4. The drum asclaimed in claim 1, characterized by means specific to each compartmentintended to create a partial vacuum.
 5. The drum as claimed in claim 1,characterized in that the ratio of the total area of the perforations,per unit of surface, to the area of the lateral surface on which theylie is greater for the first compartment than for the second.
 6. Thedrum as claimed in claim 1, characterized by a pressurized waterinjector on the portion of the roll which passes opposite the portion ofthe lateral surface of the compartment.
 7. The drum as claimed in claim6, characterized in that the water injector is disposed angularly in amanner immediately adjacent to the first compartment.
 8. A productionunit for a nonwoven material, comprising a spunbond tower with conveyorleading to a drum, characterized in that the drum is as defined inclaim
 1. 9. The installation as claimed in claim 8, characterized inthat the tower conveyor and the tangential conveyor are one and the sameconveyor.
 10. The installation as claimed in claim 8, characterized inthat the drum (24) is mounted directly downstream of the tower, that isto say without interposition of a device causing the drawing of thematerial.
 11. A method of producing a nonwoven material, characterizedin that an installation as claimed in claim 8 is used and the speed ofthe tower conveyor and/or of the tangential conveyor is greater than thelinear speed of the drum.
 12. A nonwoven material, characterized in thatthe ratio of the breaking strength in the machine direction to that inthe cross direction is less than 1.2 and in particular approximately 1.13. The nonwoven material as claimed in claim 12, characterized in thatsaid ratio is less than 1.